"Peanut Butter Bombs": An Enrichment Device for Captive Chimpanzees

R. Borman, L. Gratton-Fabbri, J. Fritz
Primate Foundation of Arizona

Environmental enrichment for chimpanzees (Pan troglodytes) should be designed to promote species-typical behaviors, mental stimulation, and occupation periodically throughout the day (Fritz & Howell 1993). This is a challenging task because the dexterous ability, intelligence, and great strength of the chimpanzees enables them to rapidly destroy items or figure things out quickly so that devices may last seconds rather than the envisioned days... or at least hours. Caregivers at the Primate Foundation of Arizona continually work to develop new enrichment. We found "peanut butter bombs" kept chimpanzees of all ages (juvenile to old adults) busy for up to three hours at a time. Some chimpanzees were even found to "work" on the device for a second time several hours after they were initially provided. They concentrate on finding ways to retrieve the food and peanut butter "lining".

The enrichment device is constructed from a destructible plastic bottle (1 to 2 liters), food treats (approximately 220 ml or 1 cup) and peanut butter (approximately 100 ml or a half cup).

Destructible plastic bottles (i.e., empty, plastic, 2 liter soft drink bottles) have been shown to be a safe and effective enrichment for chimpanzees that were more effective in maintaining interest than continued exposure to an indestructible toy (Shefferly et al. 1993). Destructible plastic bottles used at PFA are empty, sterile, irrigation bottles donated from a local hospital (thanks to our wonderful nurse volunteers!). These bottles previously contained water or saline (not antibiotic mixtures). However, 1 or 2 liter soft drink bottles can be used as well--remembering to wash and sterilize (wash with a 1:2 hypochlorine and water solution) prior to giving to the chimpanzees.

Food treats may include forage items (chicken scratch, sweetfeed, peanuts, air-popped popcorn, dry unsweetened cereals (Born et al. 1997) as well as a variety of other foods that may include nuts, marshmallows, shredded coconut, or pretzels. See Howell and Fritz (1999) for an extensive list and low-calorie options.

Peanut butter can be either a regular, low fat or a no-sugar brand depending on an individual chimpanzees dietary needs. For obese chimpanzees or when a low-calorie diet regime is preferred, a variety of moist foods can be substituted, including: honey, light corn syrup, applesauce, ketchup, mustard, tomato or bar-b-que sauce, or plain yogurt (Howell & Fritz 1999).

To make a "peanut butter bomb," follow these steps:
1. Smear the peanut butter around the inside of a destructible plastic bottle using a long knife (similar to those used to spread cake icing).
2. Squeeze the bottle together to distribute the peanut butter evenly on the inside of the bottle.
3. Add the food treats, put the lid on, and shake so that the treats stick to the peanut butter.

Each "peanut butter bomb" takes approximately 4 minutes to make.

Careful planning is needed to assure the safety and physical well-being of each individual when providing this feeding enrichment (Murphy 1994). The distribution of the "peanut butter bombs" to individual chimpanzees creates great colony excitement that may escalate into aggression (Howell et al. 1993). To overcome this potential problem, we provide the enrichment via individual feeders. This is preferable to leaving them to be found in the cage, as some chimpanzees will quickly reach for two bottles, leaving others without one. All chimpanzees at PFA are conditioned to take food or treats from his/her own feeder to avoid competition over food, stealing between animals, and feeding related aggression (Born et al. 1997). To prevent frustration and fighting over the bottles, care should be taken to ensure that each animal in a group receives one at the onset. Be sure to make a few extras in case of "stealing." Also, close attention should be paid to those animals that engage in chronic regurgitation behavior to be sure the device does not stimulate increased regurgitation activity. Regurgitation potentially has deleterious effects such as dental plaque/erosion and periodontal disease and reflux esophagitis (Howell et al. 1997). For these animals, substitution of the peanut butter with other non-sweetened foods is recommended (e.g., mustard) (Howell et al. 1997).

To work the peanut butter and treats from the bottles, chimpanzees often fashioned and used tools (straw, cardboard, a piece of plastic) in a fashion similar to termite fishing observed for wild chimpanzees (Goodall 1986). Thus, this device may offer a disposable alternative to more complex termite fishing devices (Howell & Fritz 1999). After the chimpanzees had removed all of the enrichment inside, the destructible plastic bottles also became a toy for the chimpanzees, and in some cases was even incorporated as part of their evening nesting material. We have used this device for the past 12 months with great success. It continues to keep all chimpanzees intently occupied for between two and three hours whenever offered.

Overall, we found this enrichment device to be a source of fun and excitement for the chimpanzees and a means of keeping them meaningfully occupied for long periods of time.


This project was supported by the National Institutes of Health, Division of Research Resources, Grant U42RRO3602. We also thank the volunteer, care and research staff of the Primate Foundation of Arizona for assisting in making and distributing these devices to the chimpanzees.


Born, K., Fritz, J., Trueblood, P. (1997) Chimpanzee diet at the Primate Foundation of Arizona. The Newsletter 8(4): 1-3.

Fritz, J., Howell, S. (1993) Psychological wellness for captive chimpanzees: An evaluative program. Humane Innovations and Alternatives 7:426-433.

Goodall, J. (1986) The Chimpanzees of Gombe: Patterns of Behavior. The Belknap Press of Harvard University Press: Cambridge, Massachusetts.

Howell, S. Fritz, J. (1999) The nuts and bolts of captive chimpanzee diets and food as enrichment: A survey. Journal of Applied Animal Welfare Science 2(3):2-5-215.

Howell, S., Fritz, J., Downing, S., Bunuel, M. (1997) Treating chronic regurgitation behavior: A case study. Lab Animal 26(2):30-33.

Howell, S., Matevia, M., Fritz, J., Nash, L., Maki, S. (1993) Pre-feeding agonism and seasonality in captive groups of chimpanzees (Pan troglodytes). Animal Welfare 2:153-163.

Murphy, J. (1994) The prevention of environmentally caused injury in captive chimpanzees (Pan troglodytes) at the Primate Foundation of Arizona. The Newsletter 6(2):3.

Shefferly, N., Fritz, J., Howell, S. (1993) Toys as environmental enrichment for captive juvenile chimpanzees(Pan troglodytes). Laboratory Primate Newsletter 32(2):7 -9.

Reprinted with permission of the Editor of The Newsletter.

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